Heterogametic sex

Heterogametic sex (digametic sex) refers to the sex of a species in which the sex chromosomes are not the same. For example, in humans, males, with an X and a Y sex chromosome, would be referred to as the heterogametic sex, and females having two X sex chromosomes would be referred to as the homogametic sex.[1]

However, in birds, and some reptiles, males have two Z sex chromosomes and so are the homogametic sex, while females, with one Z and one W chromosome, are the heterogametic sex. Among the insects, Lepidopterans (butterflies and moths) have heterogametic females, but in Drosophila, males are the heterogametic sex.[2]

Heterogamesis can lead to reduced or absent meiotic recombination between the sex chromosomes, and in some species this extends to the autosomes, a phenomenon called achiasmy. For example, most lineages of male Drosophila melanogaster flies are achiasmic, lacking recombination on all chromosomes, although females show recombination.[3]